Recently, progress has been made in the development of a display device (EL display device) employing a light-emitting element (hereinafter referred to as EL element) which uses EL phenomenon of a light-emitting material. An EL display device does not need a backlight unlike a liquid crystal display because the light-emitting element itself has an ability to emit light. In addition, an EL display device has the advantages of wide viewing angle, high contrast, and so on.
It is said that an EL element emits light by releasing energy when electrons injected from a cathode and holes injected from an anode are recombined at a luminescence center in an organic compound layer to form a molecular exciter and when the molecular exciter moves back to the ground state by applying a voltage with interposing the organic compound layer between a pair of electrodes. Singlet excitation and triplet excitation are known as an excitation state, and it is considered that light-emission can be obtained through both the excitation states.
Moreover, there are an inorganic light-emitting material and an organic light-emitting material as a light-emitting material which is used for an EL element, and an organic light-emitting material that requires a low driving voltage attracts attention.
However, after driving a certain period of time, an organic EL element using an organic material for the EL element has a problem in that light-emitting characteristics such as luminance and luminance uniformity degrade drastically compared to those at the beginning. The low reliability is the main factor for the limited practical application.
Moisture and oxygen which enter the organic EL element from outside are cited as one of the factors for deteriorating the reliability.
In the EL display device (panel) using an EL element, the moisture which enters an inner part leads a serious degradation in reliability to cause a dark spot, shrink and a degradation of luminance from a peripheral part of a light-emitting device. The dark spot is phenomenon in which luminance decreases partially (including nonluminescent element), and it occurs when a top electrode has a hole. In addition, the shrink is phenomenon in which luminance degrades from a pixel end part (edge).
The development has done on a display device having a structure which prevents the above degradations of an EL element. There is a method for storing an EL element in an airtight vessel to confine the EL element within an enclosed space and further providing drying agent in the enclosed space with isolating from the EL element (for example, see Patent Reference 1).
(Patent Reference 1)    Japanese published unexamined application Hei 9-148066
In addition, there is a method for forming a sealing agent on an insulator where an EL element is formed and filling an enclosed space surrounded by a cover agent and the sealing agent with filler including resin and the like to be shut out from an outer part (for example, see Patent Reference 2).
(Patent Reference 2)    Japanese published unexamined application Hei 13-203076